1. Field of the Invention
The present invention relates to an image-forming process applicable to copying machines, printers, facsimile machines, and the like, and a photosensitive member employed for the image-forming process. More specifically, the present invention relates to an image-forming process applicable to copying machines, printers, facsimile machines, and the like, comprising steps of forming a toner image on a photosensitive member having on a substrate a photoconductive layer typified by a-Si, and transferring the toner image onto a transfer-receiving medium; and relates also a photosensitive member employed for the image-forming process.
2. Related Background Art
Image forming apparatuses employing an electrophotographic process are known which forms a synthetic color image by decomposing a color image information or a multicolor information into its color components, forming a latent image corresponding to the respective color components on a photosensitive member, forming a toner image on the latent image, transferring the toner image of this color component temporarily on an intermediate image-transfer element, and further transferring onto this toner image another color component toner image in superposition. The image forming apparatus employing such an intermediate image-transfer element is useful as a color image forming apparatus, a multiple color image forming apparatus, or an image forming apparatus equipped with a color image forming mechanism or a multiple color image forming mechanism since the apparatus gives color images with sufficient superposition (registration) of component color images. Color copying machines and color printers equipped with such an image forming apparatus have come to be marketed.
Another type of image forming apparatuses are known which transfers successively color-component images of color image information or of multicolor image information directly onto a recording sheet conveyed by an image-transferring belt to output a synthesized color image or multicolor image. The image forming apparatus employing such an image-transferring belt is useful as a color image forming apparatus, or a multiple color image forming apparatus. The image forming apparatus employing the image-transferring belt is also useful as an image forming apparatus for high-speed formation.
The image forming apparatuses employing an intermediate image-transfer element or an image-transferring belt are disclosed in Japanese Patent Application Laid-Open Nos. 8-320591, 8-211757, 8-160759, 2001-51524, and so forth.
As a photosensitive material, a-Si absorbs moisture on its surface under high humidity conditions, which tends to cause smudging of the toner image to result in blurring of the formed image. Smudging the toner is not the only condition, which adversely affects the quality of the image. Other conditions affecting the quality of the image include adhering matters include various foreign matters deposited onto the photosensitive material surface such as fine dust of paper usually used as the recording sheet, organic components released from the paper, and corona products generated by corona discharge at a high voltage in the apparatus. In particular, under high humidity conditions, the deposited matter lowers the resistivity of the photosensitive material, resulting in lower sharpness of the latent image and lower quality of the recorded image. To prevent the image blurring simply and effectively, usually the moisture absorption on the photosensitive material surface is prevented by employing a heater to apply electric current throughout whole days.
Such image forming apparatuses are required to save energy and to decrease industrial waste so as not to cause environmental pollution as in Blue Angel and Energy Star Program. Therefor, a method for preventing the image blurring on the a-Si photosensitive material is demanded which does not require a waiting power of the aforementioned whole-day electricity application system. Further, elongation of the lives of the members like the photosensitive member, the intermediate image-receiving member, and image transfer belt of the electrophotography apparatus is required to decrease waste.
The a-Si photosensitive material has a significantly high hardness (Vickers hardness ranging from 1500 to 2000 kg/mm2), and is much less surface-abradable than other photosensitive materials such as organic photosensitive materials and selenium type photosensitive materials (Vickers hardness ranging from 50 to 150 kg/mm2). Specifically the abrasion loss of the a-Si by image formation of several ten thousands of sheets is only several nanometers. The organic photosensitive member or the selenium type photosensitive member is abraded at the surface during use to produce fresh surface incessantly, whereby the adverse effect of the adhering matter is reduced, even when melt adhesion of a toner or deposition of a foreign matter occurs. In contrast, the a-Si photosensitive material, which is abraded less at the surface, is liable to cause significant adhesion of the melted toner or deposition of a foreign matter depending on the constitution. Therefore, the a-Si photosensitive material changes greatly the sildability on contacting members such as a cleaning blade by adhesion of the melted toner or deposition of the foreign matter in a small amount to cause vibration (so-called chattering vibration) of the cleaning blade or uneven distribution of the load, resulting in frequent cleaning failure.
The intermediate image-transfer element or the image-transferring belt is brought into contract with the photosensitive member with a nip contact breadth of several millimeters at a contact pressure ranging from 5 to 1000 g/cm2 (0.49 to 98.1 kPa). The intermediate image-transfer element or the image-transferring belt is repeatedly attached to and detached from the copying paper sheet, which may cause fine vibration (chattering vibration). When the vibration is strong, the transferred toner image can be blurred or not to be registered to impair the image quality directly. Even when the vibration is not so strong, the energy generated by the vibration may cause toner melt adhesion, filming, adhesion of talc or paper dust onto the intermediate image-transfer element or the image-transferring belt to cause an image defect in a stripe state or a dot state, or to cause blurring of the image by high-temperature and high-humidity conditions (30xc2x0 C., 80% RH or higher) on the photosensitive member surface disadvantageously. The toner melt adhesion or foreign matter deposition tends to occur especially at the contact position (nip) of the photosensitive member with the intermediate image-transfer element or the image-transferring belt.
Hitherto, such problems have been dealt with by changing the material of or the shape of the intermediate image-transfer element of the image-transferring belt, contact conditions, and stretching conditions thereof. However, a-Si has not been studied as the factor for preventing the fine vibration, toner melt adhesion, and foreign matter deposition, so that the problem has not been solved satisfactorily.
In the recent years, electrophotographic image forming apparatuses having a printer function in addition to the copying function have come to be widely used. For such apparatuses, accessories such as a feeder mechanism and a sorter mechanism are developed. With such development, continuous image formation on 4000 sheets or more of recording sheets can be practicable in one job. In such recording operation, for example, at an image formation rate of 50 sheets (A4-size, 210 mmxc3x97297 mm) per minute, the 4000 sheet (A4-size) of image formation will be continued for 80 minutes or longer by simple calculation. Such a long time of continuous operation will elevate the ambient temperature up to about 50xc2x0 C. around the photosensitive member, and can elevate the temperature at the contact portion between the photosensitive member and the intermediate image-transfer element or between the photosensitive member and the image-transferring belt to be higher than that. In addition to the occurrence of the aforementioned fine vibration, the higher temperature at the contact portion can aggravate further the toner melt adhesion.
The a-Si photosensitive material has a semipermanent life. It is confirmed that the photosensitive member employed in a copying machine has a durability for image formation of three million to five million sheets. Therefore, for the purpose of material-saving, and running cost reduction, the intermediate image-transfer element or the image-transferring belt as the peripheral ancillary member employed with the a-Si photosensitive material should also have a sufficiently long life. However, the fatigue or deterioration of the intermediate image-transfer element or the image-transferring belt which is resulting from the fine vibration caused by repetition of contact with or separation from the a-Si photosensitive member is not sufficiently elucidated. Therefore, dramatic elongation of the life of the intermediate image-transfer element or the image-transferring belt has not been achieved.
The present invention has been made to solve the above-mentioned problems.
An object of the present invention is to enable output of an image of high quality by suppressing chattering vibration generated at the image formation site or between the members around the image formation site, and by preventing transfer deviation, toner melt adhesion, paper dust deposition, or the like.
Another other object of the present invention is to provide an image forming process in which the deterioration of the intermediate image-transfer element or the image-transferring belt is retarded to lengthen the life thereof.
Still another object of the present invention is to provide an image forming process which prevents image transfer deviation which is caused by repeated contact with, or separation from the a-Si photosensitive member, of the intermediate image-transfer element or the image-transferring belt; and prevents image blurring which is caused by toner melt adhesion or foreign matter deposition like paper dust deposition onto the photosensitive member surface.
A further object of the present invention is to provide an image forming process which enables high-speed driving of the intermediate image-transfer element or the image-transferring belt and lengthens the life thereof; and which achieves readily a higher freedom degree for selection of the construction material and the constitution of the intermediate image-transfer element or the image-transferring belt.
A still further object of the present invention is to provide an image forming process which reduces the environmental pollution by making unnecessary the heating of the photosensitive member to decrease the waiting electric power, and by other measures.
According to an aspect of the present invention, there is provided an image forming process for an electrophotographic system employing an image forming apparatus equipped with a photosensitive member having a photoconductive layer composed of a silicon-based non-monocrystalline material and a surface layer composed of a non-monocrystalline material formed successively on a peripheral face of a cylindrical electroconductive substrate, and a cylindrical intermediate image-transfer element in contact with the photosensitive member at the surface thereof, and rotating the photosensitive member and the intermediate image-transfer element at a prescribed relative speed; the process comprising an electrifying step of electrifying a surface of the photosensitive member, a latent image-forming step of forming an electrostatic latent image by protection of light onto the surface electrified in the electrifying step, a developing step for forming a toner image by deposition of a toner on the surface carrying the electrostatic latent image formed by the latent image-forming step, and an image transferring step for transferring the toner image formed in the developing step onto the intermediate image-transfer element; and repeating the electrifying step, the latent image-forming step, the developing step, and the transferring step plural times to form plural toner images in superposition on the intermediate image-transfer element, and transferring the toner images formed in superposition on the intermediate image-transfer element onto a recording sheet:
wherein the photosensitive member and the intermediate image-transfer element are brought into contact at a contact temperature ranging from 15xc2x0 C. to 60xc2x0 C. at an intended relative speed of the photosensitive member to the intermediate image-transfer element to give a kinetic frictional deviation (a standard deviation of kinetic frictional force) less than the average value of the kinetic frictional force.
According to another aspect of the present invention, there is provided an image forming process for an electrophotographic system employing an image forming apparatus equipped with plural photosensitive members having respectively a photoconductive layer composed of a silicon-based non-monocrystalline material and a surface layer composed of a non-monocrystalline material formed on a peripheral face of a cylindrical electroconductive substrate, and an image-transferring belt for holding and delivering a recording sheet with successive contact with the surfaces of the plural photosensitive members, and moving the photosensitive member and the recording sheet prescribed relative speed;
the process comprising an electrifying step of electrifying a surface of one of the photosensitive members,
a latent image-forming step of forming an electrostatic latent image by projection of light onto the surface electrified in the electrifying step,
a developing step for forming a toner image by deposition of a toner on the surface carrying the electrostatic latent image formed by the latent image-forming step,
and an image transferring step for transferring the toner image formed in the developing step onto the recording sheet; and
repeating the electrifying step, the latent image-forming step, the developing step, and the transferring step for the respective plural photosensitive members to form plural toner images in superposition on the recording sheet:
wherein the photosensitive member and the recording sheet are brought into contact at a contact temperature ranging from 15xc2x0 C. to 60xc2x0 C. at an intended relative speed of the photosensitive member to the recording sheet to give a kinetic frictional deviation (a standard deviation of kinetic frictional force) less than the average value of the kinetic frictional force.
The image forming process of the present invention prevents fine vibration of the photosensitive drum 1 and the intermediate image-transfer element 20, which can be caused by repeated contact and separation of the photosensitive member and the intermediate image-transfer element. Thereby, deviation in image transfer caused by the fine vibration can be prevented. Further, toner melt adhesion and foreign matter deposition onto the photosensitive member surface is prevented, whereby image blurring is prevented. Further, deterioration of the intermediate image-transfer element caused by the fine vibration is prevented. The temperature of the contact portion, and the kinetic frictional deviation coefficient can be controlled within the aforementioned ranges, for example by selecting the material of the photosensitive member or the intermediate image-transfer element.
Further, the fine vibration can effectively be suppressed by controlling the kinetic frictional deviation coefficient to be not higher than 0.1, where the kinetic frictional deviation coefficient is a rate of change of the ratio of the kinetic frictional deviation per unit length in length direction of the contact face to the contacting linear pressure, and the contacting linear pressure is defined as the force applied to contact the photosensitive member with the intermediate image-transfer element per unit length in the length direction of the contact-face.
The fine vibration can also effectively be suppressed by controlling the range of variation of the kinetic frictional deviation coefficient to be not more than 0.02 for change of the contact temperature of the photosensitive member with the intermediate image-transfer element from 15xc2x0 C. to 60xc2x0 C., so that the kinetic frictional deviation coefficient may not become larger regardless of temperature variation at the contact portion.
The fine vibration can also effectively be suppressed by providing a surface layer composed of a non-monocrystalline material based on silicon and/or carbon, and controlling the range of variation of the kinetic frictional deviation coefficient to be not more than 0.01 for change of the contact temperature of the photosensitive member with the intermediate image-transfer element from 15xc2x0 C. to 60xc2x0C. 
The properties of the photosensitive member in the latent image formation, the toner image formation, and the cleaning can be made stable without significant influence of environment by controlling the rate of change of the dark portion-electrifying ability to temperature change to be in the range within xc2x12%/xc2x0 C., whereby the above operation can be conducted satisfactorily. For controlling the rate of change of the dark portion-electrifying ability to temperature change to be in the range within xc2x12%/xc2x0 C., the characteristic energy in exponential energy distribution of a tail level of a valence band is preferably controlled to be in the range from 50 to 70 meV. The characteristic energy can be controlled to be in the above range, for example by selecting the material of the photosensitive layer of the photosensitive member, or selecting the film formation conditions such as the film formation speed.
The filming or the toner melt adhesion can be prevented by controlling the center-line average roughness of the surface of the photosensitive member to be in the range from 0.01 to 0.9 xcexcm, and the average inclination xcex94a to be in the range from 0.001 to 0.06. The center-line average roughness of the surface of the photosensitive member, and the average inclination can be controlled to be in the above ranges, for example by selecting the material of the photosensitive layer of the photosensitive member, or selecting the filming formation conditions such as the filming formation speed.
The present invention is also applicable, by employing the aforementioned contact conditions of the photosensitive member with the intermediate image-transfer element to the contact conditions of the photosensitive member and the image-transferring belt, to the image forming process for an electrophotographic system employing an image forming apparatus equipped with plural photosensitive members having respectively a photoconductive layer composed of a silicon-based non-monocrystalline material and a surface layer composed of a non-monocrystalline material formed successively on a peripheral face of a cylindrical electroconductive substrate, and an image-transferring belt for holding and delivering a recording sheet with successive contact with the surfaces of the plural photosensitive members, and moving the photosensitive member and the recording sheet prescribed relative speed; the process comprising an electrifying step of electrifying a surface of one of the photosensitive members, a latent image-fanning step of forming an electrostatic latent image by projection of light onto the surface electrified in the electrifying step, a developing step for forming a toner image by deposition of a toner on the surface carrying the electrostatic latent image fanned by the latent image-fanning step, and an image transferring step for transferring the toner image fanned in the developing step onto the recording sheet; and repeating the electrifying step, the latent image-farming step, the developing step, and the transferring step for the respective plural photosensitive members to form plural toner images in superposition on the recording sheet.
The photosensitive member of the present invention is employed in an electrophotographic image forming apparatus for forming an electrostatic latent image by uniform electrification of the surface thereof and projection of imaging light, depositing a toner on the electrostatic latent image to form a toner image, and transferring the toner image onto an image-receiving member. This photosensitive member has a photoconductive layer composed of a silicon-based non-monocrystalline material and a surface layer composed of a non-monocrystalline material, and has a surface which gives a kinetic frictional deviation (a standard deviation of kinetic frictional force) less than the average value of the kinetic frictional force between the photosensitive member and the image-receiving member when the photosensitive member and the image-receiving member is brought into contact at a contact temperature ranging from 15xc2x0 C. to 60xc2x0 C. at an intended relative speed of the photosensitive member to the image-receiving member.
The image forming apparatus of the present invention comprises a photosensitive member having a photoconductive layer composed of a silicone-based non-monocrystalline material and a surface layer composed of a non-monocrystalline material formed on a peripheral surface of a cylindrical electroconductive substrate, an electrifier for electrifying the surface of the photosensitive member, and imaging light projecting means for projecting imaging light onto the electrified surface to form a latent image thereon, a developing means for applying a toner onto the surface having the electrostatic latent image to form a toner image, and an intermediate image-transfer element in a cylinder shape placed to be in contact with the photosensitive member at the surfaces, wherein the image forming apparatus conducts image formation according to the image forming process as set forth above.
Another embodiment of the image forming apparatus of the present invention comprises plural photosensitive members having respectively a photoconductive layer composed of a silicon-based non-monocrystalline material and a surface layer composed of a non-monocrystalline material formed on a peripheral surface of a cylindrical electroconductive substrate, electrifiers for electrifying the surface of the photosensitive member, imaging light projecting means for projecting imaging light onto the electrified surface to form a latent image thereon, developing means for applying a toner onto the surface having the electrostatic latent image to form a toner image, and a image-transferring belt for holding and delivering a recording sheet with successive contact with the surfaces of the plural photosensitive members, wherein the image forming apparatus conducts image formation according to the image forming process as set forth above.